Flexible couplings for connecting adjoining shafts which may have their axes misaligned either through installation error or by design are well-known in the prior art and available for many applications. Most prior art flexible coupling designs, however, are limited in capability both as to durability and the degree of angular or axial misalignment permitted between the adjoining shafts (e.g. a drive shaft and load shaft). A few existing couplings utilize elastomeric material to accommodate misalignment, but they generally lack torsional stiffness and relative to their size can only transmit small amounts of torque. Conventional nonelastomeric types of flexible couplings, including the Cardan type of universal joint, permit a relatively high degree of shaft misalignment but do not provide a constant velocity relationship between the rotating shafts. Specialty universal joints have been designed to provide such a constant velocity relationship, but these joints include bearings and a seal which must be lubricated and are subject to failure.
As an alternative to prior art couplings utilizing elastomeric material, and those universal joints such as the Cardan type, link couplings have been developed to enhance angular and axial misalignment accommodation capability of the coupling while providing sufficient torsional strength. Link couplings include a plurality of individual, flexible link elements connected to one another by bolts, pins or similar means. The link elements are typically of equal length and form flexing structures consisting of a plurality of link elements connected together in a variety of symmetrical patterns including generally square or circular (i.e. octagonal, hexagonal) configurations. At least two flexing structures are joined together to form the link coupling, which in turn is connected at each end to the flange of the shafts to be joined.
The primary disadvantage of existing link couplings is that sufficient space must be provided between the link elements of adjacent flexing structures to permit insertion of the bolts or pins which join the ends of the link elements together. In addition, since the link elements are symmetrically disposed within each flexing structure, interference could occur between the bolts or pins of adjoining flexing structures in the event of axial or angular misalignment between the adjoining shafts.
One prior art solution to the problem of end connector interference between the link elements of adjoining flexing structures is described in U.S. Pat. No. 3,481,158 to Mayerjak and shown in FIG. 6. In Mayerjak the individual link elements are tapered or axially offset from end to end such that their end portions are sufficiently spaced apart to receive the connecting bolt or pin and also avoid interference with link elements of adjoining flexing structures in the event of axial or angular misalignment in the shafts to be coupled. The problem with this design is that in response to angular or axial misalignment of the adjoining shafts, the link elements in the Mayerjak and similar couplings are placed primarily in tension of compression (See FIG. 7B). As discussed more fully below, the link elements of a link coupling are much less susceptible to failure where they flex and end in response to shaft misalignment (See FIG. 7A) rather than undergoing tensile or compressive loading as is most commonly the case in the prior art.